Got confused over some of these calculus problems, any help is appreciated.
Answer choices for problem 12 are :
a) x=1
b) x=3
c) x=4
d) x=5
I currently have b chosen.

‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼️‼ ️‼️‼️‼️‼️ i have been waiting for almost an hour with no ! only answer if you absolutely know the ! explain your answer and ensure that it is you so so much!

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?

Which of the following circles have their centers on the x-axis? check all that apply.